In rural areas septic tanks in conjunction with drain fields are utilized to handle and treat residential wastewater. Septic tanks typically comprise a concrete or plastic container that receives incoming waste water or influent from the sewage drains of the residence it serves. The septic tank incorporates biologically active agents to aerobically and anaerobically digest the waste constituents of the influent that enters the tank. The digestion process causes waste particles or solids once digested to precipitate to the floor of the septic tank and form a sediment referred to as sludge. On the surface of the waste water within the tank a layer of scum forms that includes a high grease content which is unable to be dissolved into the waste water. Biological agents in the scum layer digest the waste particles in this layer which causes these particles to precipitate to the sludge layer at the bottom of the tank. A so called clear zone separates the scum layer and the sludge layer in the tank. The so called clear zone is relatively clear of suspended solid waste particles but includes particles precipitating to the bottom of the tank as the density of the particles undergoes changes during digestion. Sludge gasification further causes bubbles to form in the sludge layer which when rising to the surface also carry particles with them.
Traditionally, relatively clear waste water is discharged as effluent from the clear zone of the tank into piping that carries the effluent to a drain field or leach field. The drain field typically comprises a highly porous bed of gravel, sand or other coarse and fine aggregates. The drain field is usually disposed underground below the level of the septic tank but at a depth above the groundwater level. The drain field is efficient in allowing the wastewater to leach or percolate into the ground and eventually into the groundwater. Water leaching through the porous drain field is further filtered of solids by the gravel and sand of the drain field. Additional aerobic and anaerobic digestion of solids occurs in the drain field. By the time the wastewater has reached the groundwater supply it has been treated by the digestion process within the septic tank and from the filtering effect of the drain field.
The quality of wastewater that is permitted to enter the groundwater supply is stringently regulated in some areas to minimize the negative environmental effects that are associated with poorly treated wastewater entering the groundwater supply. These regulations have necessitated improvements to the traditional septic tank and drain field residential waste water handling system. Furthermore, as solid waste particles are discharged unintentionally from the septic tank to the drain field, the porous structure of the drain field has a tendency to become clogged with these solids thus diminishing the drainage capabilities of the drain field. Improvements have been incorporated into the traditional septic tank and drain field designs to minimize the amount of solids that are discharged into a drain field to thus insure a maximum drainage efficiency.
The two goals of maximum drain field drainage efficiency and minimum environmental impact have been best achieved in the past by the incorporation of a filter device placed in the septic tank to filter effluent leaving the tank. This filter, once utilized, insures that a minimum of untreated solid waste particles are discharged from the tank into the drain field. Additionally, maximum drain field drainage efficiency has been further advanced by the use of an incremental discharge apparatus such as a dosing siphon or pump to discharge the effluent from the tank to the drain fields. The use of an incremental discharge apparatus further necessitated the use of a filter to minimize the clogging effects of solids on the devices. Incremental discharge apparatus provide the benefit of discharging a large volume of water from the tank at spaced time increments. This type of discharge has a cleansing effect on solids accumulating within piping and within the drain field, as well.
These previous attempts at filtering the effluent that is discharged from a septic tank into a drain field have been successful in limiting the amount of untreated solid waste particles exiting the septic tank. Nevertheless, previous effluent filters had inherent inefficiencies due to their construction. Previous effluent filters are often of a design that utilizes a single filtering surface that is constructed into an enclosure and then mounted within a housing or shield. This filter design typically further incorporates a pump or other discharge apparatus that is maintained within the interior of the filter to permit the incremental discharge of filtered waste water to the drain field.
A first deficiency of the previously mentioned existing filter design is the tendency of the filter enclosure to collapse during the filtering process. The pump or dosing siphon acts to discharge the filtered water within the filter enclosure through an outlet where the water will eventually proceed to a sand filter or a drain field. The operation of the pump or dosing siphon results in suction forces, which pull inwardly on the filter enclosure. Additionally, water pressure outside the filter enclosure pushing inward on the filter enclosure also causes the filter enclosure to collapse.
Existing filters have experienced collapsing within the filter enclosures of the filters due to a design that increases the forces causing collapse, while offering little in the way of filter enclosure reinforcement.
Specifically, existing designs use relatively small inlets within the filter housing that result in high water speeds entering the housing which increases the forces pushing on the filter enclosure encouraging collapse of the enclosure. In addition to these undesirable added forces, the water entering the housing is also entering at a speed which is sufficient to pull solids into the housing, causing a build up of solids on the filter surfaces of the filter enclosure. The build up of solids on the filter surfaces limits the rate of the entry of water into the filter enclosure, which promotes collapse of the filter enclosure. The build up of solids may also contribute to collapse by providing a contact surface which water entering the filter housing interior will contact before preceding to the remaining openings within the filter surface.
The collapse or partial collapse of the filter enclosure can result in major operational problems for the filter, as well as in smaller operational inefficiencies that effect overall septic system performance. The most significant effect that collapse can cause is the entry of undigested solids from within the septic tank into the filter enclosure where the solids can plug and ruin the pump. Should the solids be discharged through the outlet by a pump or dosing siphon, the solids could plug outlet lines, sand filter distribution lines, the sand filter bed, or the drain field. Excess accumulation of solids within any of these septic system elements may cause the necessity of expensive repairs. Also possible is the discharge of undigested biological waste material that poses a health hazard to drinking water or to other ground water sources.
A second deficiency of the previous filter design is the lack of self cleaning properties. Solid waste particles that enter the housing are subject to digestion but are unlikely to be removed from the housing due to the absence of an outlet for solids that are drawn into the housing. The accumulation of solid waste particles will cause the inefficient operation of the filter, and eventually will cause the entire filter to plug which can ruin the pump if the problem is not detected immediately. This accumulation is also problematic during routine maintenance of the filter. A filter with a large amount of solids accumulation can plug drainage check valves which prevents the drainage of water from the filter during removal of the filter from the septic tank. The filter in this situation is extremely heavy and very difficult to remove from the septic tank for inspection. Accumulated solids, of course, add further weight to the filter.
A third deficiency in the previous waste water filter design has been the inability to back flush the filter. This feature is a necessity considering the inherent tendency of the previous filter designs to clog with solid particles quite easily. The inability to back flush the filter in a simple manner also results in expensive labor costs to the septic tank owner when the filter eventually plugs.
In lieu of the deficiencies of previous effluent filter designs there is clearly a need for a filter that: includes a filter enclosure that will not collapse under any circumstance, minimizes the clogging effects of accumulating solid waste particles on the filter surface by providing self cleaning characteristics to the filter which minimizes costly maintenance, and can be easily back flushed.